CALIS-1 and CALIS-2 are pulse sequences for the accurate calibration of the RF field strength for an indirectly observed spin are introduced. CALIS-2 is intended for calibration of e.g., 13C or 15N pulses on natural abundance samples whilst CALIS-1 is recommended primarily for enriched samples. Both experiments can be performed without prior knowledge or guess of the RF field strength and no delays in the pulse sequences are critically dependent on coupling constants.


For theta= pi/2 the signal goes through a zero crossing. The same phasing is applied to all of the spectra recorded with the different vales of theta. The delay tau = 2(1JIS)-1 and the delay tau'= tau-5 theta. The delay delta = delta0-5 theta/2

The gradients are set so as to fulfil either of the equations:

1) gammaIG1 - (gammaI + gammaS)G2 - (gammaI - gammaS)G3 = 0

2) gammaIG1 - (gammaI - gammaS)G2 - (gammaI + gammaS)G3 = 0

For I and S being 1H and 13C respectively the first equation is fulfilled for G1=+5, G2=-2 and G3=+10. The gradient Gp is optional and can be of any size.

The recommended phase cycle is an even number of steps out of:

  • phi 1 = {x, -x, -x, x},
  • phi 2 = {x, x, 4(-x), x, x},
  • phi 3 = {4(x), 4(y), 4(-x), 4(-y)}
  • Receiver phase {x, -x}.


example CALIS calibration spectra a) shows an example calibration of the 13C RF field strength using the CALIS-2 sequence on mannose and shows both the alpha and beta anomeric signals. b) as for (a) but using the CALIS-1 sequence. The clean zero crossing illustrates how effectively any residual signals from protons attached to 12C are suppressed.


  1. Andrew J. Benie, Ole W. Sørensen New methods for calibration of the RF field strength for indirectly observed nuclei J. Magn. Reson. 180 317-320 2006

Code and procedures for Varian and Bruker.

Document: CALIS (index.shtml)
Last modified: 2006-05-15